The present invention relates to a wireless communication apparatus used in such a mobile communication system that a mobile communication is carried out by employing a portable telephone and the like. More specifically, the present invention is directed to a wireless communication apparatus used in a transmitter, and a transmission power control method executed between a mobile station and a base station in a mobile communication system.
Conventionally, transmission power control techniques are known in such a mobile communication system with employment of a portable telephone and the like. That is, in this mobile communication system, while information is transferred, transmission power of the own mobile station is controlled in response to a distance between a base station and the mobile station so as to maintain constant electric power of a signal reached to the base station. Thus, the transmission power control techniques are capable of reducing interference occurred between communication channels and are capable of improving frequency utilization efficiencies.
In particular, in a CDMA (Code Division Multiple Access) type mobile communication system using the spread spectrum technique, corresponding to one sort of multiple access type communication systems for multiplexing a plurality of communication channels, a single frequency band is commonly used by a plurality of users. As a result, there are large possibilities that a so-called “near-far problem” may occur, namely one communication signal having low electric power may be masked by another communication signal having high electric power. Therefore, the following problem may occur. That is, a communication signal of another communication station may deteriorate as an interference signal wave line quality of the own communication station. To solve this problem, various transmission power control techniques have been conventionally investigated, or considered. More specifically, as the transmission power control systems capable of following interference signals which are instantaneously varied, such a transmission power control system constituted by a closed loop is known in this technical field. In the CDMA communication system, more specifically, the high-linearity transmission power control with the wide dynamic range (for example, 70 to 80 dB) is strongly required. Furthermore, the high precision of transmission power while the high power transmission is carried out is required in the wide-band CDMA (W-CDMA etc.) communication system in IMT-2000, so that the transmission power control is required in higher precision. This wide-band CDMA communication system is presently studied as the next generation mobile communication system.
FIG. 5 is a flow chart for describing one example of the conventional transmission power control method realized by the closed loop. In the case that a base station is communicated with a mobile station, the base station determines a transmission power control bit based upon reception power of a reception signal wave (namely, desirable signal wave) sent from the mobile station (step S11). The base station inserts this determined transmission power control bit into a transmission signal, and then, transmits this resultant transmission signal to the mobile station. The mobile station receives the signal transmitted from the base station, and extracts the transmission power control bit from the received signal (step S15), and then, controls a variable power amplifier employed in the own mobile station in response to the instruction of this transmission power control bit so as to change the transmission power (step S16).
Similarly, the mobile station determines a transmission power control bit based upon reception power of a reception signal wave (namely, desirable signal wave) sent from the base station (step S14). The mobile station inserts this determined transmission power control bit into a transmission signal, and then, transmits this resultant transmission signal to the base station. The base station receives the signal transmitted from the mobile station, and extracts the transmission power control bit from the received signal (step S12), and then, controls a variable power amplifier employed in the own base station in response to the instruction of this transmission power control bit so as to change the transmission power (step S13).
Since such a transmission power control is carried out, the reception power in the base station and also the reception power in the mobile station can be kept substantially constant irrespective of locations of the mobile station.
As previously explained, in order to perform the transmission power control in such high precision in accordance with the conventional transmission power control method, the transmission power control range corresponding to the value (1 unit) of the transmission power control bit is required to be reduced. However, if the transmission power control range is decreased, then the rapid, or sudden variation of the reception power cannot be followed by this conventional transmission power control method. As a result, there is such a problem that the precision of the transmission power control operation is deteriorated.
Also, in order that the transmission power control operation is carried out in such high precision in accordance with the conventional transmission power control method, the variable power amplifier operable in the high precision is necessarily required. Also, the variable power amplifier must be controlled in high precision. However, in the case that such a high-precision variable power amplification control operation is realized by employing the high-precision variable power amplifier, the following problems may occur. That is, the circuit scale is increased, so that the power consumption amount thereof is increased and further, the wireless communication apparatus becomes bulky in size, resulting in deteriorations of portabilities thereof.